I think the boys look plausibly like Lois and Hal's children, yes. I actually think most of the boys--Malcolm, Dewey, and Jamie (though it's hard to tell for sure yet with him)--look more like Lois than Hal, while Francis definitely looks more like Hal imo. Reese, I think, looks like a cross between his parents, with a leaning towards Lois.
And as for blond hair...
Simple Explanation of Recessivity in Genes: Recessive genes get passed on regardless of whether the individual displays the effect of the gene (whether it's eye/hair colour, or a disorder like haemophilia). If a man's father has blue eyes and his mother has brown eyes, and this man gets brown eyes, he still has a recessive gene for blue eyes. Now, if he marries a brown-eyed woman with the same genetic ancestral background as himself, there's actually a rather good chance of them producing blue eyed kids, since both parents have a recessive blue-eyed gene inherited from their parents.
Because of the above, I don't see it as unusual that Francis and Dewey have blond hair. They simply could've inherited it from their grandparents.